Flow Injection Detection of Tetracyclines by Electrocatalytic Oxidation at a Nickel-modified Glassy Carbon Electrode

The electrocatalytic oxidation of tetracyclines in an alkaline solution at a nickel-modified glassy carbon electrode was investigated. The response of the modified electrode was characterized by voltammetry and flow injection. Subsequently, it was used for amperometric detection of tetracyclines in a flow injection system. The preparation of the modified electrode is carried out by simple deposition of NiII solution onto the glassy carbon-based electrode. The detection is based on the measurement of anodic current generated by the catalytic oxidation of the antibiotics at the surface of the electrode through the formation of a high-valent, oxyhydroxide species (NiOOH) at +550 V (versus Ag/AgCl). The modified electrode offers a stable and reproducible catalytic oxidation current for these antibiotics without recourse to pulsed waveform potential. Rapid quantification at the mg 1-1 (ppm) level is achieved. Standard calibration graphs for tetracycline, doxycycline, oxytetracycline and chlortetracycline yielded linear ranges of 2.5-80, 2.5-100, 2.5-100 and 2.5-100 mg l-1, respectively. Detection limits (S/N = 3) of (0.03, 0.92, 0.34 and 1.81 mg l-1 were obtained for tetracycline, doxycycline, oxytetracycline and chlortetracycline, respectively. The electrode was applied for the determination of the four antibiotics in single-component drug formulations.